has anyone seen this error before? trying to import a Sales Order: Please enter value(s) for: Subject

Do you have mandatory field Subject ? Or check on the form : Navigate to Customization > Forms > Transaction Forms. 1. Edit the preferred Sales Order form. 2. Navigate to Printing Fields tab > Header sub tab. 3. In the Company Name field, do you have mark the Print/Email checkbox?? 4. If yes In the Label field, enter the subject to use when emailing orders.

Also could be a script or workflow trying to send an email from each SO and there is no subject for the email

in the advanced settings for add/update in the second step of import wizard you can turn off the 'run workflow option' - that should sort it if its a workflow trying to send an email e.g.